The longest I think I stopped writing was probably about a month during a time I thought I wasn't "qualified" to be a writer.
Let me explain. I was so excited about submitting to a particular editor. Then I read somewhere that this editor liked working with authors who were "educated." Well, that burst my bubble since I never graduated college. I was crushed. After reading that, I started reading author bios and noticed how many successful writers had a college degree. Needless to say, I felt like a complete idiot, the nerd trying to fit in with the popular kids.
Thanks to a writer friend who had convinced that I didn't need a college education (nor did this editor only work with those who had a college education), I wiped the tears, put the chocolate away and continued to write and submit. I found a Harlequin editor who liked my style and story premises, however, the stories weren't fitting into the line I was targeting. Another writer friend told me to "write longer stories", so I did, and that's when I really fell in love with writing.
The rejection letters don't stop me from writing anymore and only after I finish a story, I take a break to read and catch up on house cleaning.
Advice to those who get knocked down and need a helping hand to get back up, remember this...for every minute you don't write, another writer is and he/she could be writing a similar story as the one you're working on. So the sooner you get back to writing, the sooner you can get that manuscript in front of an editor before someone else does.